Acid catalysts have found widespread use in the conversion of numerous organic chemical species to various end products. The organic chemical reaction in which the acid is used may be, for example, a dehydration, esterification, etherification, aldol condensation, enolization, oxidation, dehydrogenation, acetalization, or alkene hydration reaction. Typical acids include sulfuric, carboxylic, and phosphoric acids, particularly when a polar solvent is used. For non-polar solvents, the sulfonic acids (e.g., methanesulfonic acid and p-toluene sulfonic acid) are typically used.
Unfortunately, the wastes generated from these acid catalysts are environmentally harmful, and thus, require substantial time and cost in their removal, conversion to salt species, and storage as waste. Moreover, after conversion, the acids generally cannot be recovered in suitable form for further chemical reactions.
For this reason, efforts have been made in finding alternative acid catalysts having fewer drawbacks. For example, silica-based acid-functionalized catalysts have been used. However, the silica acid catalysts generally require filtration for their removal, as well as use of organic solvents, both of which result in significant labor, cost, and waste management.